Microsoft’s Internet Explorer development team has confirmed there will be a browser extension system for Project Spartan, meaning developers will be able to extend its functionality with software that can be built directly into the browser.

“Yes. We’re working on a plan for extensions to a future update to ‘Project Spartan,’ the developer relations team for IE said during a Q&A chat on Twitter Tuesday.

The news is significant since it indicates some type of a developer ecosystem will evolve around the browser, allowing functions to be added that are not supported natively. Such extensions could allow tabs to be given specific color codes, or allow bookmarks to be catalogued in new ways, or Web pages to be archived locally.

Google Chrome and Mozilla Firefox have their own systems for adding functionality to those browsers. The Microsoft developers didn’t say if the Spartan extensions will be available through the Windows 10 Store, which is being remodeled for the new OS.

The team also eliminated any doubt that Spartan will become the default Windows 10 browser. “IE will be available for Windows 10 and can [be] enabled by the user,” they said in one tweet.

“Spartan is the successor for both desktop and modern IE,” they said in another. “It will be finger friendly on touch machines,” indicating that Spartan will likely follow Microsoft’s Continuum design methodology, discussed at the Windows 10 preview events.

While Spartan will be the default browser in Windows 10, Microsoft has indicated that users will have the option to enable IE if they wish. In the latest Windows 10 Technical Preview build, “Internet Explorer 11” is clearly listed as one of the features users can turn on or off by checking a box.

The team didn’t describe Tuesday how Windows 10 users will activate IE 11, but in Windows 8.1, “legacy features” such as DirectPlay, and add-ons such as Windows Media Player, are added by means of a dialog box called “Turn Windows Features on or off.”

Spartan didn’t ship with the Technical Preview of Windows 10, but a Web page that displays when the OS preview is installed indicate that the first developer builds of the browser will be offered separately in the coming days.